The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to methods of forming self-aligned gate contacts and cross-coupling contacts for field-effect transistors and structures for field effect-transistors that include self-aligned gate contacts and cross-coupling contacts.
Contacts may provide vertical electrical connections to features of semiconductor devices, such as the gate structures of a field-effect transistor. Self-aligned contacts are formed in contact openings that are constrained during etching by the configuration of adjacent structures, e.g., sidewall spacers on adjacent gate structures, as opposed to being constrained by a patterned resist. Gate caps are provided over the gate structures to protect the metal gate during the etching of the contact openings for the self-aligned contacts.
Self-aligned contacts connected with a metal gate of a field-effect transistor may be categorized into distinct types. One type of self-aligned contact, which is only connected with the metal gate, is electrically isolated from nearby features, such as the semiconductor material forming source and drain regions of the field-effect transistor. Another type of self-aligned contact cross-couples the metal gate with the semiconductor material forming the source or drain regions of the field-effect transistor, and may be found, for example, to provide cross-coupling of inverters in a static random access memory bitcell. When forming a self-aligned cross-coupling contact, the top surface of the metal gate is opened by at least partial removal of the gate cap.
A self-aligned contact providing cross-coupling may be weak if the constituent conductor over the metal gate is overly thin. Such over thinning may occur when polishing to planarize the conductor that is deposited to form the self-aligned cross-coupling contact. In addition, the semiconductor material forming the source or drain region is exposed to the etching process that at least partially removes the gate cap to open the top surface of the metal gate, which can damage the semiconductor material.
Improved methods of forming self-aligned gate contacts and cross-coupling contacts for field-effect transistors and structures for field effect-transistors that include self-aligned gate contacts and cross-coupling contacts are needed.